Previously, there have been many attempts to create an improved heart assist device. Specifically, many of the previous inventions in this field have focused on providing a left ventricular assist device (LVAD) which is implantable.
Most of the devices and systems that have targeted the permanent implant market have focused on developing blood pumps that are suitable for beyond the general average life expectancy of the patient. This leads many implantable left ventricular assist devices (LVADs) to be over-engineered and being extremely expensive to manufacture.
Many of the LVADs used for permanent implantation are manufactured from stainless steel, nitinol, or titanium alloys. All of these exotic metals are relatively expensive to machine and difficult manufacture.
Additionally, there have been many previous inventions that target short term usage (typically less than 6 hours) and are typically not implantable. Also these inventions tend to be only suitable for applications during heart bypass operations or similar emergency situations. A majority of these types of devices are constructed of polymeric materials. A majority of these devices are designed to provide maximum pumping efficiency of the pumping fluid. However, many of these types of devices fail to reduce shearing forces on the pumping fluid. In LVADs, the pumping fluid is typically blood and wherein the LVAD imparts a relatively high shearing force on the blood, the blood tends to clot or haemolyse.
The previous short term devices typically result on patient complications or serious adverse events occurring for usage extending beyond about 8-12 hours. Also many of these short devices rotate at higher relative levels of rotations per minute (RPM) than the longer term devices and this may further exasperate the haemolysis effect.
U.S. Pat. No. 6,609,883—Woodard et al describes a blood pump fabricated mainly from Titanium-6 Aluminum-4 Vanadium (Ti-6A1-4V) coated with amorphous carbon and/or diamond-like coatings. In particular, the pump housing of this blood pump is metallic and includes a magnetic drive motor acting on a hydrodynamic impeller within the pump housing. One of the disadvantages with this invention is that as the pump housing is entirely constructed of metal, electrical eddy currents form between the motor stators and permanent magnets positioned within the impeller. These electrical eddy currents significantly reduce the electrical efficiency of the blood pump and may lead to increased power consumption.
Another U.S. Pat. No. 6,158,984—Cao et al describes a modified blood pump in which structural members are inserted within the pump housing between the motor stators and the impeller. These structural members are constructed of a biocompatible, corrosion resistant, electrically non-conductive (insulative) ceramic material. One of the disadvantages with the structural members being comprised of ceramic material is that ceramic material is relatively expensive and difficult to construct. The ceramic material may include a diamond like coating which may be particularly costly to produce and prone to flaking.
Another US Patent Application 20070270633—Cook et al describes a centrifugal blood pump with a hydrodynamically suspended polymeric impeller. This device includes an impeller of a difficult manufacturing shape with dimensional stability issues relating to the tights tolerances of the impeller blades in relation to the housing. Minor dimension changes in use or in moulding of this invention may possibly lead to pump stop or clotting issues.
It has been previous known to this field, that rotary blood pumps may be entirely constructed from polymeric material except for the motor components. However, pumps that are entirely constructed of polymeric materials may lack the desired: wear resistance or strength, fluid impermeability and bio-resistance necessary for this type of application. These types of pumps commonly warp or distort due to fluid absorption limiting their usefulness.
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.